Vector: Implement find, find_if, find_first_matching in terms of AK::find*

Problem:
- The implementation of `find` is coupled to the implementation of `Vector`.
- `Vector::find` takes the predicate by value which might be expensive.

Solution:
- Decouple the implementation of `find` from `Vector` by using a
  generic `find` algorithm.
- Change the name of `find` with a predicate to `find_if` so that a
  binding reference can be used and the predicate can be forwarded to
  avoid copies.
- Change all the `find(pred)` call sites to use `find_if`.

Libraries/LibCore/ArgsParser.cpp

@@ -109,7 +109,7 @@ bool ArgsParser::parse(int argc, char** argv, bool exit_on_failure)
             index_of_found_long_option = -1;
         } else {
             // It was a short option, look it up.
-            auto it = m_options.find([c](auto& opt) { return c == opt.short_name; });
+            auto it = m_options.find_if([c](auto& opt) { return c == opt.short_name; });
             ASSERT(!it.is_end());
             found_option = &*it;
         }

Libraries/LibMarkdown/Text.cpp

@@ -69,7 +69,7 @@ String Text::render_to_html() const
             { "b", &Style::strong },
             { "code", &Style::code }
         };
-        auto it = open_tags.find([&](const String& open_tag) {
+        auto it = open_tags.find_if([&](const String& open_tag) {
             if (open_tag == "a" && current_style.href != span.style.href)
                 return true;
             if (open_tag == "img" && current_style.img != span.style.img)

Libraries/LibTLS/ClientHandshake.cpp

@@ -398,7 +398,7 @@ ssize_t TLSv12::handle_payload(ReadonlyBytes vbuffer)
                 }
                 payload_res = handle_certificate(buffer.slice(1, payload_size));
                 if (m_context.certificates.size()) {
-                    auto it = m_context.certificates.find([&](auto& cert) { return cert.is_valid(); });
+                    auto it = m_context.certificates.find_if([](const auto& cert) { return cert.is_valid(); });
 
                     if (it.is_end()) {
                         // no valid certificates